Presently, the conventional telephone set employs either a rotary dial mechanism or a multifrequency tone pad for generating signals representing a desired numeric or alphanumeric sequence. The conventional rotary dial mechanism is a mechanical device embodying switching structure which interrupts direct current flowing through the dial contacts so as to generate a series of electrical pulses in a pulse train. Such pulses typically have a forty percent make time (high energy) and a sixty percent break time (low energy), the latter also identified as an interpulse interval. The tone pad, when used in place of the rotary dial mechanism, generates tone signals composed of two fundamental frequencies; these frequency signals are decoded into a digital form representing the numeric or alphanumeric sequence. The pulse train from either the rotary dial mechanism, or the digital signals after decoding from the tone pad, connects to central office equipment that operates to interconnect a calling party to the remote station identified by the sequence. To ensure that the central office equipment operates properly, the rotary dial mechanism must operate at the correct dial speed and produce a pulse train having the correct pulse width (break time), or the tone pad must generate the correct fundamental frequencies.
The characteristics of telephone switching equipment in a central office location require that the incoming dial pulses, and the periods between them, meet certain timing criteria. One of these criteria is the pulse repetition rate, that is, the rate at which the pulse interval periods occur. A second timing criteria widely used in checking pulse trains is the so called percent break, defined as the ratio of the interpulse interval, or break period, to the repetition period (the sums of the pulse and interpulse interval durations). It is particularly desirable to test incoming dial pulses simply and quickly for these two criteria; the apparatus for making such tests should enable a speedy determination that the mechanism generating the pulse train is operating as desired.
The pulse repetition rate, also identified as the dial speed for a rotary dial mechanism, is defined in pulses per second and heretofore has generally been measured as the repetition rate averaged over the entire pulse train rather than on a pulse by pulse basis. However, since the telephone equipment to which the pulse train is connected only operates reliably when the pulse train has a specified minimum repetition period, it has been found that it is more desirable to check the repetition rate on a pulse by pulse basis rather than on the basis of an average over the entire pulse train. It has also been found to be more desirable to check the pulse and interpulse interval periods directly on the basis of individual time durations, rather than by an averaged measurement.